The invention is directed to tooling for filament winding and more particularly a mandrel with improved means for reversing the fiber runs at selected low angles.
Traditionally filament winding tooling depicted in drawing FIG. 1 denoted as prior art incorporates a central section composed of a body of revolution, i.e. a cylinder, cone, etc, bounded by hemispherical end domes connected to the center shafts or poles. The smooth surface translation between the central section and the end domes usually prevents the placement of very low angle windings, i.e. less than 10 degrees, due to slippage of the fiber tows.
When vary low angle wrappings are desired, two common approaches are employed.
The first approach utilizes dowel pins protruding from the circumference of the ends of the central section as shown in drawing FIG. 2. The pins are used to secure the fiber tows in place prior to rotation of the mandrel 10 and the reversal of the horizontal carriage motion, not shown. The use of dowel pins has several disadvantages. Establishment of the proper pin spacing along the circumference is crucial to assuring complete coverage of the tool surface without excessive gaps between adjacent fiber bands. The dowel pin spacing is limited to the band width chosen and the band width itself cannot be too large or movement of the fiber tows within a single band will result in unacceptable gaps between adjacent bands. The use of dowel pins also introduces additional machining time and cost during fabrication of the mandrel as numerous pin holes are required to attach the dowel pins. This typically involves a center drill, rough drill and reaming operation for each dowel pin hole required along the circumference of each end of the mandrel. This approach is often limited to reusable metal mandrels as the dowel pin hole fabrication operations would be required for each use of disposable mandrels constructed of plastic, sand, etc., and the inherent fragility of these materials limits most machining operations.
The second approach to produce low angle fiber placement involves the use of staged resin pre-impregnated unidirectional fiber material (prepreg tape). The prepreg tape is either placed in pieces manually along the length of the mandrel or a prepreg tape laying head is used in conjunction with the filament winding operation. The need to include a manual operation in order to provide low angle fiber placement defeats the efficiency of high volume material placement inherent with filament winding. The use of prepreg tape laying head requires a halt in production to change over the mandrel supply and delivery system from wet filament winding set-up to a dry prepreg arrangement and back again or the expensive and complex addition of a dual filament winding/tape laying delivery system.
There has not been a completely successful means and method and particularly a low cost convenient means and method for placement of very low angle winding until the emergence of the present invention.